Strain-specific characteristics INTRODUCTION

While the nutritional value can be manipulated, other qualities favourable for aquaculture use can be obtained by selection of strains and/or their cross breeds. Although until recently over 90 % of all marketed cysts originated from the Great Salt Lake, Artemia cysts are commercially available from various production sources in America, Asia, Australia and Europe. A knowledge of the characteristics (both genotypic and phenotypic) of a particular batch of cysts can greatly increase the effectiveness of its usage in a fish or shrimp hatchery.

SIZE AND ENERGY CONTENT

The nutritional effectiveness of a food organism is primarily determined by its ingestibility and, as a consequence, by its size and form (see further : chapter 4.3.3.). Data on biometrics of nauplii from various Artemia strains are given in Table 4.1.2.

Table 4.1.2. Size, individual dry weight and energy content of Artemia instar I nauplii from different cyst sources hatched in standard conditions (35 g.l^-1,25°C)

cyst source length

Many strains can be differentiated on the basis of their biometrical characteristics. In spite of small variations between batches of the same strain, possibly caused by environmental and/or processing factors, generally the cyst diameter of different production batches of the same strain remains rather constant. Other biometrical characteristics such as cyst volume, cyst dry weight, instar I-naupliar length, individual naupliar weight and naupliar volume, energy content etc., show a high correlation with the cyst diameter. As a consequence, biometrical parameters, in particular cyst diameter, are good tools to characterize Artemia strains, and to help to define the origin of unknown or even mixed cyst samples.

Some general correlations can also be made between sibling species and size:

parthenogenetic Artemia produce large cysts, A. tunisiana large cysts with a thick chorion, A.

franciscana and A. persimilis small or intermediate cysts with a thin chorion.

HATCHING QUALITY

Comparative studies of the hatching behaviour of cysts of different origin show a considerable variation in hatching percentage, rate and efficiency. However, none of these parameters is strain specific as they are influenced by a wide array of factors like harvesting, processing, storage and hatching techniques, as well as production conditions affecting the parental generation. For optimal use of Artemia in aquaculture the hatching characteristics of any batch of cysts being used should be known. More information in this respect is given in chapter 4.2.5.2.

GROWTH RATE OF NAUPLII

Standard culture tests with brine shrimp from different geographical origin show important differences in growth rate even within the same sibling species, but not among batches of the same strain (Table 4.1 .3.). Although in the field the population growth of Artemia (i.e. after inoculation) is determined by lots of factors, selection of a strain with a high potential growth rate will have a positive impact on maximal production output.

TEMPERATURE AND SALINITY TOLERANCE

Both temperature and salinity significantly affect survival and growth, the effect of temperature being more pronounced. A broad range of temperatures and salinities meets the requirements for >90% survival. Strains from thalassohaline biotopes share a common temperature area of preference in the range 20-25°C where mortalitiesaare <10 %.

Interaction between temperature and salinity is limited; substantial differences in tolerance have been recorded at low salinities (around 5 g.l^-1) and high temperatures (30-34°C). At elevated temperatures the survival of the GSL strain is significantly higher than for other strains.

Table 4.1.3. Growth of Artemia nauplii from different cyst sources under standard culture conditions (7 days, darkness, 10 instar I nauplii/25 ml, 35 g.l^-1, 25°C, fed with Dunaliella viridis)

cyst source growth expressed as % recorded for reference strain (SFB, batch 1 )

San Francisco Bay, CA-USA, batch 1 96 San Francisco Bay, CA-USA, batch 2 96

Macau, Brazil, batch 1 98

Macau, Brazil, batch 2 103

Great Salt Lake, UT-USA, batch 1 125 Great Salt Lake, UT-USA, batch 2 127

Shark Bay, Australia 95

Chaplin Lake, Canada 130

Tanggu, Bohai Bay, PR China 110

Aibi Lake, PR China 105

Yuncheng, PR China 109

LIFE HISTORY TRAITS AND REPRODUCTIVE CAPACITY

Life history and reproductive characteristics of Artemia strains are important factors when an introduction of brine shrimp in a new habitat is considered, especially when competition with a local strain is to be expected. These competitive abilities are related to factors like the length of reproductive, pre- and post-reproductive period, total lifespan, number of offspring per brood, broods per female, time in-between broods etc. In general New World (bisexual) populations have a very large number of offspring per brood, a large number of offspring/day/female and a fast development time to sexual maturity, which favours this group to Old World bisexual and parthenogenetic Artemia.

Age at first reproduction is a key factor determining the population growth rate, and the rate of colonisation of new environments with limited nutrient resources. Consequently, if environmental preferences and nutritional factors don't interfere, New World bisexuals generally outcompete parthenogenetic strains, the latter in their turn predominating over Old World bisexuals. Inoculation experiments in natural habitats therefore require prior screening of candidate strains and of eventual local populations, as well as the study of prevailing environmental conditions. Uncontrolled introduction of Artemia may thus lead to a decrease of natural variability. Therefore, before inoculation of Artemia in a habitat with a local strain is undertaken, sufficient cyst material of the local population must be collected and stored in order to safeguard its gene-pool.

NUTRITIONAL VALUE

In the late seventies, when many fish and shrimp hatcheries started to go commercial, switching from one source of Artemia to another provoked unexpected problems (Table 4.1.4.). Very significant differences in production yields were even obtained with distinct Artemia batches of the same geographical origin. Especially the pattern of total lipids and fatty acid composition, as well as the metabolization of fatty acids in the Artemia, seemed to differ widely from strain to strain, and even from batch to batch, as a consequence of the fluctuations in biochemical composition of the primary producers (mainly unicellular algae) available to the adult population. Cyst products from inland resources are more constant in composition, be it however at suboptimal low levels. Appropriate techniques have thus been developed to improve the lipid profile of deficient Artemia strains, taking advantage of the indiscriminate filter-feeding behaviour of Artemia.

Applying simple methods lipophilic compounds can be easily incorporated into the Artemia before being offered as a prey (see chapter 4.4.).

A number of other compounds also appear to be variable from strain to strain: nutritional components such as total amount of free amino acids, pigments (canthaxanthin), vitamin C, minerals and trace elements, as well as contamination with chemicals such as pesticides and heavy metals. In most cases these variations are not strain specific, but just correspond to different production conditions. Despite this, their effects on larviculture success are usually far less significant.

Table 4.1.4. Growth and survival of fish and crustacean larvae fed with Artemia nauplii from different cyst sources

cyst source species tested survival growth

San Francisco Bay, CA-USA, various batches

Macau, Brazil, various batches Mysidopsis bahia + +

Cancer irroratus + +

Beardmore, J.A., Pilla, E.J., and Thomas, K.M. 1994. Genetic variation in Artemia : speciation, reproductive mode and potential for exploitation. In: Book of abstracts of contributions presented at the International Conference “Improvement of the commercial production of marine aquaculture species”. G. Gajardo and P. Coutteau (Eds), Puerto Montt, Chile, 5-9 December 1994.

Browne, R.A. and Bowen, S.T. 1991. Taxonomy and population genetics of Artemia. In: Artemia Biology. Browne, R.A., P. Sorgeloos and C.N.A. Trotman (Eds), CRC Press, Boca Raton Ann Arbor Boston, USA, pp 221 -235.

Browne, R.A. and Halanych, K.M. 1989. Competition between sexual and parthenogenetic Artemia: a re-evaluation (Branchiopoda, Anostraca). Crustaceana, 57 (1) :57-71

Browne, R.A., Li, M., Wanigasekera, G., Simonek, S., Brownlee, D., Eiband, G. and Cowan, J. 1993.

Ecological, physiological and genetic divergence of sexual and asexual (diploid and polyploid) brine shrimp (Artemia). Trends in Ecology: 1-114.

Browne, R.A., Sallee, S.E., Grosch, D.S., Segreti, W.O. and Purser, S.M. 1984. Partitioning genetic and environmental components of reproduction and lifespan in Artemia. Ecology, 65 (3):

949-960.

Lavens, P. and Sorgeloos, P. 1987. The cryptobiotic state of Artemia cysts, its diapause deactivation and hatching, a review. In: Artemia Research and its Applications, Vol. 3. Sorgeloos, P., D.A.

Bengtson, W. Decleir and E. Jaspers (Eds), Universa Press, Wetteren, Belgium, pp 27 -63.

Léger, Ph., Bengtson, D.A., Sorgeloos, P., Simpson, K.L. and Beck, A.D. 1987 . The nutritional value of Artemia, a review. In: Artemia Research and its Applications, Vol. 3. Sorgeloos, P., D.A.

Bengtson, W. Decleir and E. Jaspers (Eds), Universa Press, Wetteren, Belgium, pp 357 -37 2.

Persoone, G. and Sorgeloos, P. 1980. . General aspects of the ecology and biogeography of Artemia.

In: The brine shrimp Artemia. Vol. 3. Ecology, culturing, use in aquaculture. Persoone, G., P.

Sorgeloos, O. Roels and E. Jaspers (Eds), Universa Press, Wetteren, Belgium, pp 3-24.

Pilla, E.J.S and Beardmore, J.A. 1994. Genetic and morphometric differentiation in Old World bisexual species of the brine shrimp (Artemia). Heredity, 7 2: 47 -56.

Tackaert, W. and Sorgeloos, P. 1991. Semi-intensive culturing in fertilized ponds. In: Artemia Biology.

Browne, R.A, P. Sorgeloos and C.N.A. Trotman (Eds), CRC Press, Boca Raton Ann Arbor Boston, USA, pp 287-315.

Triantaphyllidis, G.V., Zhang, B., Zhu, L. and Sorgeloos, P. 1994. International Study on Artemia. L.

Review of the literature on Artemia from salt lakes in the People’s Republic of China.

International Journal of Salt Lake Research, 3:1-12.

Vanhaecke, P., Tackaert, W. and Sorgeloos, P. 1987 . The biogeography of Artemia: an updated review. In: Artemia research and its applications. Vol. 1. Morphology, genetics, strain characterisation, toxicology. Sorgeloos, P., D.A. Bengtson, W. Decleir and E. Jaspers (Eds), Universa Press, Wetteren, Belgium, pp 129-155

4.1.3. Literature of interest